1. Field of the Invention
The present invention relates to a method and apparatus for measuring the profile of a three-dimensional object and, more particularly, to improvements in a method and apparatus for measuring a profile in a noncontact manner in which a light beam is projected onto the surface of a target and scanned over the surface of the target and the profile of the target is measured from the optical image of the surface of the target.
2. Description of the Prior Art
Applications of a method of measuring the profile of a three-dimensional object utilizing an optical system have been expected not only in the fields of CAD/CAM and computer vision and as the eyes of robots, but also in somatometry and measurement and analysis of natural objects in the medical and dressmaking fields, and in other various fields including graphic design.
A stereo system is known as a typical system in several optical methods of measuring a profile. According to the stereo system, photographs of a target are taken from a plurality of visual angles by a plurality of industrial cameras, and a profile is obtained from these images.
This system is based on the principle of binocular stereoscopy, and the image data of the taken photographs are input in the form of lightness signal data over the entire imaging plane. In order to extract only a necessary profile from these data, it is inevitable to detect the correspondnng points, which requires various kinds of image processings and, hence, a large amount of memory capacity and a long processing time. Therefore, this system has not been embodied as a high-speed and simple apparatus.
Among other conventional systems, a light intersection system is most general and has been considered to be considerably practical. In this light intersection system, a spot-like or slit-like light beam is projected to a target, and image signals based on the optical image of the surface of the target are input to a computer by an image grabber. Then, from the positional information on the optical image on the imaging plane obtained as a result of processing these signals and the relative positional relationship between the light beam and the image grabber, the space coordinates of the surface of the target are obtained.
That is, according to the conventional light intersection system, for example, a light beam deflected for scanning is projected onto the surface of a target, and the optical image of the surface of the target formed by the light beam is inputted to a computer in the form of image signals by a scanning type image input device such as an ITV camera or a CCD camera.
As a result, according to this conventional system, the position of the optical image of the target is specified by subsequently electrically scanning the entire imaging plane, and this procedure is repeated for each light beam deflected for scanning. The profile of the three-dimensional object is measured from the multiplicity of data obtained in this way.
The conventional light intersection system, however, is disadvantageous in that it is necessary to scan the entire imaging plane every time each point of the surface of a target is detected and specified and, hence, it takes a very long time to measure the profile, thereby making it impossible to measure the profile in real time. Generally, the time required for scanning one field is approximately 1/60 to 1/30 second in the case of an ordinary industrial TV camera, and such slow scanning operation makes it almost impossible to measure the profile of an object at real time or to measure a moving object.
Especially, in order to measure a three-dimensional object with a practicably sufficient resolving power, it is necessary to scan many fields, so that very slow scanning by deflecting a light beam is necessary in the conventional light intersection system which requires the electrical scanning of the entire imaging plane, as described above. It is therefore impossible to measure the profile with sufficient resolving power at the real time.